Using Aerosol OT in Hexane Solution to Synthesize Calcium Nitrate Self-Healing Refined Microcapsules for Construction Applications

Abstract

The micro-encapsulation procedure of calcium nitrate in urea-formaldehyde shell is well known. The most recent developed method for the synthesis of the calcium nitrate self-healing micro-capsules was based on the in-situ polymerization using water-in-oil emulsion. Although the microcapsules’ yield was significantly improved using this approach, incorporating the micro-capsules into concrete mixes has been found to reduce strength. One potential strength reduction cause might be the presence of sulfonic acid as a component in the continuous (oil) phase. As the anionic surfactant, Aerosol OT (AOT) has been widely used to prepare water-in-oil emulsions and to form aggregates in non-polar solvents; submicron calcium nitrate refined microcapsules were synthesized using AOT in hexane solution. While the aqueous phase in the original encapsulation procedure has not been altered, the continuous organic phase was prepared by dissolving AOT in hexane. The prepared microcapsules were characterized using Scanning Electron Microscopy (SEM). The preliminary assessment of the effect of incorporating of the refined microcapsules into cementitious materials has been carried out by preparing mortar mixes using 75% capsules’ concentration (by weight of cement). The reported yield values, average shell thickness, and average diameter of the prepared microcapsules were found satisfactory. Moreover, the mortar samples containing calcium nitrate refined microcapsules that were prepared using the proposed method did not experience significant reduction in their mechanical properties. Hence, such encapsulation procedure may be adopted for further investigation of the self-healing efficiency in cementitious materials of the microcapsules prepared using the proposed procedure. Future work shall be directed towards this end.